Measurement of flow velocity for hydrogen introduced into a wall-stabilized argon arc

Small solid particles are usually used as tracers for the measurement of flow velocity of a fluid. In the case of a high-temperature thermal plasma, sometimes it is difficult to use solid tracers due to the loss by vaporization caused by strong heat transfer from the plasma. If gaseous tracers could be used, it would compensate for the difficulty in using conventional solid particle tracers. To investigate the feasibility of gaseous tracers, hydrogen was used as a gaseous tracer for flow velocity measurement of a well-stabilized argon are plasma. Propagation of Ha line emission along the are axis was observed by high speed photography using a CCD camera with bandpass filters. The propagation velocity was 30 to 100 m/s which was influenced by the flow rate of argon. The Peclet number was calculated for the experimental condition. The result shows that the effect of the diffusion on the mass transport is smaller than that of the flow. This means that the propagating velocity of the Ha line emission closely corresponds to the flow velocity of the argon are plasma with the added hydrogen. The measured velocity and the estimated average flow velocity of argon are plasma were in good agreement. The principle of the gaseous tracer was confirmed, although further work will be needed for practical use. (C) 2001 Scripta Technica, Electr Eng Jpn, 135(1): 15-23, 2001.